Currently, 85% of the world's crude oil production is by means of primary and secondary recovery, with an approximately 35% recovery of the oil existing in the reservoir (Babadagli T., 2007: Development of mature oil fields—A review. J. Petroleum Science Engineering 57: 221-246). Since the recovery rate is low, enhanced recovery methods have been implemented, often referred to as EOR (Enhanced Oil Recovery). Oil Recovery can be classified into three processes:
1. Primary recovery oil is produced using the energy from the oil or gas reservoir and/or forcing it through using pumps.
2. Secondary recovery consists of an increase in pressure in the reservoir by means of an external energy source. For instance, fluid injection in the rock of the reservoir is a common process to carry higher volumes of petroleum to the surface. More than 25% of petroleum is recovered this way.
3. Tertiary or EOR oil recovery from a reservoir after recovery by primary or secondary methods, involve reservoir heating or use of chemicals. Procedures for tertiary recovery include injecting into the reservoirs, miscible solvents, hydrocarbonated gases or carbonic gas, as well as soda water, tensoactives or hydrosoluble polymers, including any type of process used to supply the reservoir of an additional source of energy to enhance petroleum recovery compared to that produced during primary and secondary recovery processes.
Reservoir production starts with the natural flow of crude oil due to the energy in the reservoirs, and later water and gas injection, like in the secondary recovery processes. Tertiary or EOR methods are not widely used, because of the high costs and complexity of required equipment. Such processes are used to maximize long term economic value of the reservoir.
Low recovery of petroleum in reservoirs is due to several factors: low permeability, high viscosity of oil, high interfacial tension within water and petroleum, and high capillarity forces, that result in low mobility (Chisholm et al., 1990: Microbial enhanced oil recovery: interfacial tension and gas-induced relative permeability effects. SPE: 20481, 8).
Since secondary recovery processes have economic and/or practical limitations in their application, the development of innovative technologies is required to further exploit processes (Planckaert M., 2005: Oil reservoirs and oil production. In Petroleum Microbiology. Ollivier B. and Magot M. (Ed.), ASM Press, Washington D.C. 3-19). Tertiary or EOR processes used to increase the productive life of oil wells; including water or other liquid injection to force oil towards production oil wells. The properties of oil can be modified by adding surfactants that can in turn modify the wettability of the rock containing the oil (Mukherjee et al., 2006: Towards commercial production of microbial surfactants. Trends Biotechnol. 24 (11):509-15; Singh et al., 2007: Surfactants in microbiology and biotechnology: Part 2. Application and aspects. Biotechnology Advances 25:99-121; Youssef et al., 2007: In situ biosurfactant production by Bacillus strains injected into a limestone petroleum reservoir. Appl. Environ. Microbiol. 73 (4):1239-47).
Hydrocarbon recovery by means of microbial processes is a type of tertiary or EOR technology. This technology has been shown to increase the production of oil in wells and reservoirs, and is environmentally-friendly and economically efficient (Maure et al., 1999: Microbial enhanced oil recovery pilot test in Piedras Coloradas field, Argentina. SPE 53715; Bryant R and Lockhart T. P., 2002: Reservoir engineering analysis of microbial enhanced oil recovery. SPE Reservoir Evaluation & Engineering, 365-374; Nazina et al., 2008: Regulation of geochemical activity of microorganisms in a petroleum reservoir by injection of H2O2 or water-air mixture. Microbiology 77 (3): 324-333).
Extremophile microorganisms can live in environments considered unsuitable for most organisms, including petroleum reservoirs that are typically characterized by high temperature, salinity and pressure. Therefore, the indigenous microorganisms from a reservoir have been selected for optimal survival under such extreme conditions. (Monastersky R., 1997: Deep dweller microbes thrive far below ground. Science 151 (13):192-193).
In International Patent Application No. WO 2009/009382 A3, “Process for enhanced oil recovery using a microbial consortium”, published on Jan. 15, 2009, Soni et al. propose a method that includes selection of the oil well. The characteristics considered for the application of such a process were oil well depth <3,048 m (10,000 ft), temperature <90° C., pressure <300 Kg/cm2, pH from 4 to 9 but preferably from 6 to 8, and total salinity of formation water <12% (<10% NaCl). Microbiological prospecting and selection of microorganisms were carried out by using 4 different culture media supplemented with nutrients, minerals and a carbon source. This process involved the injection of the media and microorganisms into a selected oil well and incubation of the microbial consortium for one to three weeks to facilitate release of oil and increase recovery.
U.S. Published Patent Application No. 20070092930 A1 entitled “Process for enhanced recovery of crude oil from oil wells using novel microbial consortium”, published on Apr. 26, 2007 by Lal et al. discloses a process for hydrocarbon recovery, wherein a mixed culture of thermophiles, barophiles and acidogenic anaerobe bacteria were developed in culture media containing nutrients, minerals and a complex carbon source. Incubation and enrichment of the microorganisms was carried out at temperatures ranging from 70 to 90° C. The microorganisms were obtained from samples collected under strict anaerobic conditions. During enrichment of the samples, production of CO2, CH4, biosurfactants, fatty acids and alcohol metabolites were observed, indicating growth and development of microorganisms. Recovery experiments were carried out in packed granular systems and Berea sandstone cores, with 148 mD permeability, 19% porosity and a 27.9% residual saturation. Oil recovery was reported to be 8.9%. U.S. Published Patent Application No. 20070181300 A1 entitled “System and method for preparing near-surface heavy oil for extraction using microbial degradation” published on Aug. 9, 2007 by Bushe and Rollins discloses a heavy oil recovery system that uses bacteria and fungi, with the addition of nutrients. The application field of this patent is oil located near the reservoir surface, implying that the invention is used at relatively low temperatures and pressures. The mechanisms that influence oil mobility include a decrease in viscosity, production of metabolites, such as gases and acids, and hydrocarbon biodegradation. The patent application does not disclose oil density intervals or API Gravity for applicability of the invention.
U.S. Pat. No. 5,163,510 entitled “Method of microbial enhanced oil recovery” and issued Nov. 17, 1992 to Sunde discloses a method to enhance oil recovery in rock by using exogenous aerobic microorganisms and nutrient (N and P) addition. Experiments describe the use of cores with 700 mD permeability and incubation at 45° C. to obtain a residual oil recovery of 9% after secondary recovery. The characteristics of the oils to which the process can be applied are not specified. Mechanisms attributable to recovery are: CO2 and biosurfactants production, as well as hydrocarbon degradation.
In many of the stated references, oil recovery using microorganisms has been carried out in high permeability systems, such as Berea sandstone with a 148 mD permeability or systems with higher permeability (packed systems). On the other hand, such references do not disclose the permeability of the system used or other important characteristics of the oil, such as viscosity, API Gravity and pressure conditions, or referring that the microorganisms are resistant to high pressure conditions.
There is a continuing need for technologies focused on low permeability systems (lower than 100 mD), high pressures (up to 154.6 Kg/cm2; 2,200 psi) and high temperatures (above 60° C.), which are conditions in many Mexican fields.